This carries a surprising amount of complexity despite only being
possible in the case where monitor updating failed during the
processing of funding_generated. Specifically, this requires
handling rebroadcasting funding_locked once we successfully persist
our monitor again.
As an alternative we could never send funding_signed when the
monitor failed to persist, but this approach avoids needless
delays during funding.
Instead, return a Duration and let the user do the work of waiting.
This is one of only a handful of steps to make us
mostly-syscall-free, at least enough to run in WASM according to
elichai.
This fixes a rather subtle case handling RAAs when we don't
generate a response due to a previous monitor update failure, but
would otherwise send a CS response. We need to still set
AwaitingRemoteRevoke on the channl in question, but previously did
not. Found by chanmon_fail_consistency fuzz test with the failing
test converted and added manually.
